Use ctypes and some python magic to unpack C/C++ bitfields struct dynamically.

bitfields_struct.cpp

typedef struct __attribute__ ((packed)) Data {
        uint32_t temperature_internal: 10;
        uint32_t temperature: 10;
        uint32_t pressure: 12;
 
        uint32_t humidity: 10;
        uint32_t temperature_soil: 10;       
        uint32_t battery_level: 7;
        uint32_t leaf_wetness: 4;
        uint32_t pad0: 1;
 
        uint32_t rainrate: 8;
        uint32_t pad1: 24;
} data_t;

ctypes_unpack.py

import binascii
import json
import pprint
from ctypes import c_uint32, LittleEndianStructure

def ctypes_unpack(fields, data):

    def _get_fields():
        return fields

    class Frame(LittleEndianStructure):

        _fields_ = _get_fields()

        def __init__(self, _):
            super().__init__()

        def __new__(cls, buf=None):
            return cls.from_buffer_copy(buf)

        def _to_dict(self):
            return {field[0]: getattr(self, field[0]) for field in self._fields_}

        @property
        def fields(self):
            return self._to_dict()

    frame = Frame(data)
    return frame.fields


def main():
    with open('sensors.json') as f:
        result = json.loads(f.read())

    fields = [(k, eval(v['type']), v['bits']) for k, v in result.items()]

    # frame = decode(fields, binascii.unhexlify('f514d570c7e5923feb000000'))
    frame = ctypes_unpack(fields, binascii.unhexlify('fa3025e4e8f4f21b75000000'))
    pprint.pprint(frame)

if __name__ == '__main__':
    main()

sensors.json

{
  "temperature_internal": { "type": "c_uint32", "bits": 10, "max": 50, "min": -30},
  "temperature": { "type": "c_uint32", "bits": 10, "max": 50, "min": -30},
  "pressure": { "type": "c_uint32", "bits": 12, "max": 1100, "min": 800},

  "humidity": { "type": "c_uint32", "bits": 10, "max": 100, "min": 0},
  "temperature_soil": { "type": "c_uint32", "bits": 10, "max": 50, "min": -30},
  "battery_level": { "type": "c_uint32", "bits": 7, "max": 12, "min": 0},
  "leaf_wetness": { "type": "c_uint32", "bits": 4, "max": 15, "min": 0},

  "rainrate": { "type": "c_uint32", "bits": 8, "max": 255, "min": 0}
}